In an imaging apparatus such as a camera and a video camera, it is desired that images of various subjects present at a wide range of distances from an optical imaging system be captured with less blur. That is to say, it is desired that a depth of field of the optical imaging system be increased. The depth of field can be increased by adjusting an aperture stop so as to increase the F-number. However, increasing the F-number leads to an insufficient amount of light of a subject optical image being received by a light receiving surface. Thus, measures must be taken, such as decreasing a shutter speed and increasing the ISO sensitivity of a film or an area sensor. However, decreasing the shutter speed leads to a difficulty in capturing a moving subject. Further, increasing the ISO sensitivity causes problems such as increased noise in a captured image.
For this reason, suggestion has been made that a phase mask is used to regularly disperse light beams so as to cause a response of an optical transfer function of the optical imaging system to be substantially insensitive to a wide range of object distances, and a dispersed image is captured, which subsequently undergoes a deconvolution processing operation, thereby removing blur (see Patent Documents 1 and 2). According to the invention disclosed in Patent Document 1, the image of the subject within such a range of object distances gets blurry. However, since the light beams are regularly dispersed, it is possible to reduce the blur in images of subjects present at various distances by a restoration processing operation and to increase the depth of field.
However, according to the inventions disclosed in Patent Documents 1 and 2, the response of the optical transfer function of the optical imaging system by the phase mask was low. Consequently, there was a problem in that performing a restoration processing operation so as to sufficiently reduce the blur resulted in increased noise.